advent_of_code/year2017/
day20.rs

1use crate::input::Input;
2
3// Parse input in the format "A=<211,-141,-45>".
4fn parse_vector(input: &str) -> Option<(i32, i32, i32)> {
5    if input.len() > 3
6        && let Some(stripped) = input[2..]
7            .strip_prefix('<')
8            .and_then(|s| s.strip_suffix('>'))
9    {
10        let mut number_parts = stripped.split(',');
11        let x = number_parts.next()?.parse::<i16>().ok()?;
12        let y = number_parts.next()?.parse::<i16>().ok()?;
13        let z = number_parts.next()?.parse::<i16>().ok()?;
14        return Some((i32::from(x), i32::from(y), i32::from(z)));
15    }
16    None
17}
18
19pub fn solve(input: &Input) -> Result<u32, String> {
20    let mut particles = Vec::new();
21
22    for (line_idx, line) in input.text.lines().enumerate() {
23        let on_error = || format!("Line {}: Invalid format", line_idx + 1);
24
25        let mut parts = line.split(", ");
26        let position_part =
27            parse_vector(parts.next().ok_or_else(on_error)?).ok_or_else(on_error)?;
28        let speed_part = parse_vector(parts.next().ok_or_else(on_error)?).ok_or_else(on_error)?;
29        let acceleration_part =
30            parse_vector(parts.next().ok_or_else(on_error)?).ok_or_else(on_error)?;
31
32        particles.push((position_part, speed_part, acceleration_part));
33    }
34
35    for _ in 0..500 {
36        particles = particles
37            .iter()
38            .filter_map(|particle| {
39                if input.is_part_two()
40                    && particles
41                        .iter()
42                        .filter(|other_particle| other_particle.0 == particle.0)
43                        .count()
44                        > 1
45                {
46                    None
47                } else {
48                    let new_speed = (
49                        particle.1.0 + particle.2.0,
50                        particle.1.1 + particle.2.1,
51                        particle.1.2 + particle.2.2,
52                    );
53                    let new_position = (
54                        particle.0.0 + new_speed.0,
55                        particle.0.1 + new_speed.1,
56                        particle.0.2 + new_speed.2,
57                    );
58                    let new_acceleration = particle.2;
59                    Some((new_position, new_speed, new_acceleration))
60                }
61            })
62            .collect();
63    }
64
65    if input.is_part_one() {
66        Ok(particles
67            .iter()
68            .enumerate()
69            .fold((0, i32::MAX), |acc, (idx, particle)| {
70                let dist = particle.0.0.abs() + particle.0.1.abs() + particle.0.2.abs();
71                if dist < acc.1 { (idx, dist) } else { acc }
72            })
73            .0 as u32)
74    } else {
75        Ok(particles.len() as u32)
76    }
77}
78
79#[test]
80pub fn tests() {
81    let real_input = include_str!("day20_input.txt");
82    test_part_one!(real_input => 91);
83    test_part_two!(real_input => 567);
84}
advent_of_code/year2017/day20.rs

advent_of_code/year2017/
day20.rs
